1. Field of the Invention
The invention generally relates to in-system testing of components and more specifically relates to testing of components while those components are functioning, or testing components in an operating range the components do not operate in during normal system operation.
2. Description of the Related Art
Over the years, several systems have been employed for land seismic exploration. A common system that is currently in use employs vibroseis trucks to impart seismic energy in the form of acoustic waves into the ground. The frequency of these acoustic waves are typically in the range of 10-100 Hz.
Seismic energy reflected from acoustic impedance discontinuities is detected by geophones and the output of the geophones is connected to an instrument box. In the instrument box are signal conditioning devices, A/D converters, a means of recording the data or sending it via telemetry to a recorder at the Recording truck, power supply and a processor.
Because the geophones are often connected together and to the instrument box with cables having connectors, the system is susceptible to a variety of problems. Among other things, rodents and cows can chew on the cables or trample them. Naturally, other forces of nature and other defects in the system can also cause problems. Animals, rainwater, and other forces can lead to degradation in performance of the system. This degradation can be manifested by increased cable resistance, short or open circuits, cross-talk between sensors or chains of sensors, leakage of signals to ground, and other similar manifestations.
As a result of these problems, a variety of tests need to be performed to determine if there is any degradation in the system. In some cases, such as leakage of signals to ground or increased resistance, a compensation factor can be determined. In other cases, such as short or open circuits, data cannot be collected until the problem is repaired, and previously collected data may need to be ignored. Determining when these measures are necessary requires testing connectivity of the sensors to the instrument box, leakage of the sensors and/or their cables, and cross-talk between the cables and their associated cables.
One example of a leakage test would involve sending a test signal to a sensor and observing what signal was received back from the sensor. The changes in characteristics from the test signal to the received return signal would give an indication of how the signal is distorted when it passes along the connection between the sensor and the instrument box or other receiving system. An example of a cross-talk test would involve sending a test signal to a first sensor and observing the signal received from a second sensor with no direct connection to the first sensor. If no signal from the second sensor appeared to be related to the test signal, no cross-talk would be occurring, whereas if a strong signal from the second sensor appeared to be related to the test signal, cross-talk would be occurring. With regard to connectivity, or an open and short circuits test, again a test signal could be sent to a sensor or string of sensors and the response of that sensor or string of sensors observed. Whatever signal or response was received (or not received) would give an indication of whether the sensor in question was not functioning properly. Those skilled in the art will appreciate that other methods of implementing these tests exist.
However, these tests are typically performed during the downtime of the operation, when no information signals are being recorded. Normally, such systems have used modes of operation that always had intervals of dead time, i.e. time when no receive signal activity occurred, during which instruments could be tested to determine their quality. With the introduction of the slip-sweep vibroseis operation there is no interval of dead time during actual operation of the system in which the components can be tested to verify that they are working correctly while the system operates. The slip-sweep vibroseis operation involves sweeping a signal generator through a range of frequencies on a repeated basis, such that each successive sweep overlaps the previous sweep, resulting in not only a constant generation of some signal, but some intervals during which two or more signals are generated simultaneously.
One embodiment of the present invention is a method of testing a component including operating the component; sending an out-of-band test signal to the component; and observing a response of the component to the out-of-band test signal. Alternatively, the invention may be an apparatus for testing a set of one or more components comprising a signal generator, the signal generator coupled to one or more of the components, the signal generator for generating test signals outside of an operating frequency band of interest; and a receiver, the receiver coupled to one or more of the components, the receiver for receiving signals outside of the operating frequency band of interest.
Likewise, the invention may be an apparatus for testing a set of one or more components including generating means for generating a test signal, the generating means coupled to at least one of the components, the generating means configured to generate a test signal at a frequency outside an operating frequency band of interest of the components; and receiving means configured to receive a response to a test signal, the receiving means coupled to at least one of the components.
Another alternative embodiment of the present invention is a method of testing a component including operating the component, triggering a test signal, the component sending an out-of-band test signal while the component operates, and observing the out-of-band test signal while the component operates.
Additionally, an alternative embodiment of the present invention is a method of testing including operating the component using signals appropriate to the intended purpose of the component, sending a test signal different from the appropriate signals to the component while operating the component, and observing a response of the component to the test signal while operating the component.